1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to a semiconductor device of the size of a semiconducter chip and which includes the; chip and a flexible substrate.
2. Description of the Related Art
First of all, a package known as uBGA ( Ball Grid Array ) manufactured by Tessera Co., will be described below.
A semiconductor device called TCC ( Tessera-Compliant-Chip), which is published in "Nikkei Micro Device, page 98-102, May 1994, and is disclosed in U.S. Pat. No. 5,258,330, has a wiring structure very similar to that of a two-layer TCP (Tape Carrier Package). A flexible wiring substrate used for this package is manufactured in processes similar to those employed to make a TCP tape.
The conventional semiconductor device described above is shown in a sectional view in FIG. 1.
A flexible wiring substrate 32 has the same structure as the so-called two-layer TCP-composed Cu-polyimide using no adhesive agent, in which Au is sputtered and plated on the film 31 made of polyimide, and the wiring 33 and the lead 37 are formed by being patterned. Via-holes formed in the film 31 are filled with Ni-plating or solder. Further, Ni or the solder accumulates so that the semispherical bump 34 which is higher than the film 31 is formed. The surface of the bump 34 is coated with thin Au plating. The film 31 is fixed to the semiconductor chip 36 with the elastic adhesive agent 35. The film 31 serves also to seal the semiconductor chip 36. The lead 37 which extends from the film 31 attached to the semiconductor chip 36 is connected to the Al pad or Au pad on the semiconductor chip 36 by means of a thermo-compression bonder using jointly ultrasonic waves. Thus, the lead 37 is made to be gull-wing shaped. This semiconductor device attaches the protection frame 38 to the circumference of the semiconductor chip 36. The inside of the protection frame 38 is filled with resin so that the lead 37 is sealed.
This package has a feature in that it is excellent as KGD ( Known Good Die ) technology. Specifically, since the package is an area array package which is called a uBGA, the package can be subjected to a burn-in test after it is attached to the testing substrate for use in a PGA ( Pin Grid Array ). Thus, this test is carried out easily prior to mounting.
Next, TBGA ( Tape Ball Grid Array ) manufactured by IBM Co., disclosed in Published Unexamined Japanese Patent Application Heisei 1-307236, will be described with reference to FIG. 2, as a conventional semiconductor device.
It has been proved that the adoption of very thin flexible materials for the substrate carrier is effective for solving the problem of the thermal expansion difference between the semiconductor chip and the carrier. FIG. 2 is a sectional view of a semiconductor device whose structure is devised considering the above fact. In the semiconductor device of FIG. 2, the insulative material layer 22 made of a material such as teflon is molded on the metal carrier layer 21, and the via-hole 23 is formed in the insulative material layer 22. The metal film 24 is formed on the insulative material layer 22. Then, the necessary circuits are formed on the metalized insulative material layer 22 and the portion where the connection terminals for electronics devices and the like are bonded. In FIG. 2, the semiconductor chip 25 is connected to these circuits. The circuit patterns are formed also in the metal carrier layer 21, and the BGAs composed of the bumps 26 for connection to the mounting substrate are arranged on the metal carrier layer 21. These bumps 26 are formed by soldering or thermo-compression bonding. The semiconductor device in FIG. 2 has a structure that the carrier is composed of a flexible material. Therefore, the carrier has an effect on the connection to the mounting substrate affected by the thermal expansion difference.
In the first conventional semiconductor devise shown in FIG. 1 and described above, the elastic adhesive agent 35 has to be filled in between the flexible wiring substrate 32 and the semiconductor chip 36. In the second conventional semiconductor device shown in FIG. 2 and described above, a carrier which is far larger than the semiconductor chip 25 is used so that a large mounting area is needed.
Furthermore, in any of the semiconductor devices shown in FIGS. 1 and 2, a high positional precision is necessary for the connection between the semiconductor chip and the carrier and thus the positioning of both is difficult. The smaller the connection pitch of the connection portion of the semiconductor chip and the carrier is, the more severe the above problem is.